One method I have used to off set any KH/Gh effects has been using some ground peat added to the bottom layer of onyx.
Around a handful per sq ft or so, it's not exact
But even with KH3/GH5 tap water, the KH/Gh are stable and have been since I set the tank up about 3 months ago.
I have a good deal of onyx in a 75 gallon.
I also recommend adding some mulm/detritus to the bottom layer(1 inch or so) from an existing tank. Vacuum the gravel good and let the mulm settle to the bottom of the bucket and decant off the clear water. Save this "mulm". Add this fresh to your tank when you need it and feed some into your filter to seed it as well.
The substrate is the one variable that's difficult to reproduce from the start and this adds precisely what the substrate needs.
The flourite and the onyx are also exceptional substrates for non CO2 planted tanks. These, unlike peat and soil based substrates, have only become nicer and more stable over time not needing to be "recharged" or redone.
You can have depths up to 12 inches if you want to slope the gravel or build mounds.
I think perhaps the three main points over the years I've use these two products are: heavy-easy to plant and keep the plants rooted: stability: and good color in a number of species that simply could not be met through water column nutrient dosing alone. I don't worried about or mess with the substrate nor worried about pulling any muck up or fret over a 1 inch slope in the front going up to 12 inches in the rear.
And Greg will answer your questions on the Forums(Where does he get the time?
)
Now I know Greg as well but I started raving about this stuff long before I knew him. Even Amano used it when he came here. It was heavier than his powersand and did not have the peat preadded, but it was 75% less $ than powersand also.
Regards,
Tom Barr
